1. Field Of The Invention
This invention relates to bearings for rotary and/or reciprocating shafts, and more particularly to bearing liners constructed from wear resistant plastic material having a low coefficient of friction.
2. Background Of Related Prior Art
A moving shaft supported by a bearing requires a low friction surface where the shaft contacts the bearing. The low friction surface may be attained for example by the application of a lubricant substance such as oil or grease, or by employing a bearing liner constructed from low friction material, or by combining a lubricant oil or grease with the use of a low friction bearing liner.
Bearing liners constructed from wear resistant low friction materials such as nylon, acetal, or polytetrafluoroethylene are known in the art. For example, Thomson, U.S. Pat. No. 3,033,623 discloses a fluorocarbon sleeve bearing comprising a layer of low friction material bonded to the inside of a metal support strip which is coiled into a cylindrical shape with its ends in close adjacency to each other.
Modern bearing liners for rotary and/or reciprocating shafts are molded single piece constructions of low friction plastic which are shaped as hollow cylinders. Similar to the Thomson U.S. Pat. No. 3,033,623 bearing liner, such modern bearing liners typically have a separation or gap extending from one end of the cylinder to the other. This separation or gap allows, inter alia, the bearing liner to be compressed into a smaller diameter so that it may be axially inserted into a housing bore.
In applications where the motion of the shaft exerts axial forces upon the bearing liner, especially with reciprocating shafts, the bearing liner must have a means for retaining it within the housing bore to prevent it from being ejected. Flanges provide such a means. In certain applications a bearing liner will have one or more flanges extending radially from the end or ends of the bearing. The flange or flanges may be external to the housing bore and overlap the edge of the bore to provide for retention of the bearing liner, or the flange may be received into an undercut in the inside surface of the housing bore where it is engaged when the bearing liner is inserted into the bore.
Notwithstanding, problems sometimes arise in applications such as pneumatic and hydraulic linear actuators when the motion of the shaft is not in perfect alignment with the axis of the bearing. Pivoting motion in a reciprocating shaft, or precession of a rotating shaft, will place great stress at the corner of the bearing liner where the flange is located. Liner flanges often break under the forces exerted by non-axial shaft motion. Non-axial motion of the shaft occurs because there must be some clearance between the shaft surface and the liner in order to permit movement of the shaft.
Clearly, then, an improved bearing liner would not only extend the useful life of the liners made of the type of materials currently being used, but would also permit the construction of liners from low friction materials which heretofore could not be used because of their lower mechanical strength.